In arc welding, filled wire or rod or filled wire or rod electrodes, as these terms are defined in German Industrial Standard DIN 8571 (March 1966 edition) comprise tubular metal members containing a filling of an arc stabilizing, protective-gas-producing, slag forming, alloying and/or fluxing material generally in pulverulent or other packed form.
Such electrodes can be used to strike an arc with a workpiece for deposit welding or can be used as a filling metal by being fed into an arc struck between a nonconsumable electrode and the workpiece.
Basically, two groups or filled wire or filled wire electrodes can be mentioned. In a first of these groups the tubular structure is not completely closed, i.e. the structure is made from strip material and the ends are bent, folded, overlapped or otherwise brought together to provide a seam which is not completely sealed.
A second group of electrodes has a sealed seam and hence the enclosed filling is protected from the environment completely.
This second group of electrodes has the advantage that it can be subjected to a wet process for coating it with copper, the copper serving as a lubricant when the electrode wire is fed through a welding machine guide and as a conductivity-promoting layer reducing the contact resistance between the welding current source and the electrode. The wet process does not involve penetration of moisture to the filling of this type of electrode and such electrodes can be used with particular advantage for hydrogen-controlled welding since the filling does not pick up moisture.
The nonsealed electrodes, however, either cannot be subjected to wet copper coating because of moisture penetration to the filling, the moisture being difficult if not impossible to remove, or can be subjected to such coating only if the wetting of the filling is immaterial, thereby limiting the welding operations for which such electrodes can be used.
For example, when the continuously formed electrodes are cut into lengths for use as manual welding electrodes, and are to be sheathed with flux agents or, more generally, compositions which can be termed welding assists, the coating method must avoid moisture penetration to the filling.
The present invention is primarily concerned with sealed electrodes and mention can be made of the methods of fabrication disclosed in the German patent documents Nos. 1,602,260, 25 15 342 and 27 19 357.
The systems described in German patent documents Nos. 1,602,260 and 27 19 357 operate intermittently and thus are disadvantageous because they cannot be used for the continuous production of the welding wire. A continuous method is used in German patent document No. 25 15 342.
It should also be noted that nonsealed electrodes cannot be readily rolled, drawn or otherwise reduced in diameter to diameters less than 1.6 mm. Smaller diameter electrodes are of principal interest commercially.
In the use of filled electrodes and filled wires for the deposition of weldment upon a workpiece, consideration must be given to the nature of the transfer of material from the wire to the pool of welding. The electromagnetic fields should be rotationally symmetrical and should permit such transfer in the form of uniform drops.
A disadvantage of conventional sealed electrodes is that the sealing process, generally by welding, appears to result in a breakthrough of material inwardly beyond the gap or some other distortion of the electrode.